This invention relates generally to air conditioning units and, more particularly, to the positioning of a fan in the outdoor coil of a thru-the-wall, packaged air conditioning system.
In residential air conditioning and heat pump systems, the evaporator and condenser sections are commonly split with one being located indoors and the other one outdoors, and with the two being connected only by refrigerant lines. In such systems, the indoor coil is normally placed in the attic or the like. In contrast, for higher capacity systems such as those used in commercial buildings, both the indoor and outdoor units are placed in the same container to constitute a so-called packaged system which is placed outdoors, normally on the roof of the building. A variation on this approach is the so-called thru-the-wall units wherein, because of the aesthetics or other structural limitations, the packaged unit is placed in the wall of a building with one coil communicating with the outdoor air and the other coil communicating with the indoor air by way of fans.
With such a thru-the-wall arrangement, it will be recognized that, unlike the outdoor coil for a split system or a packaged unit located on the roof, the path of the outdoor air must be made to flow inwardly and then be turned 180 degrees to flow outwardly after it passes through the outdoor coil. This can be done with a "blow-thru" arrangement wherein the fan is at the intake opening, or with a "draw-thru" arrangement wherein the fan is at the outlet opening. If a blow-thru arrangement is employed, then it is necessary to maintain a distance between the fan and the coil in order to have a reasonable distribution of airflow through the coil. This, in turn, requires additional space which may not be available in such a thru-the-wall installation.
Another problem with the blow-thru arrangement is that after the air has been blown through the coil and made the 90 degree turn to exit the unit, the "throw" (i.e. the velocity of the air leaving the unit) is substantially reduced, and the hot discharge air will tend to be drawn back into the intake and recirculated.
If a draw-thru arrangement is employed, then the height of the outlet opening must necessarily be as large as the diameter of the fan. Assuming a limited wall opening height, if the height of the outlet opening is made large enough to accommodate the diameter of the fan, then the height of the heat exchanger coil must be reduced. This problem has been addressed, to some extent, by the tipping of the draw-thru fan such that its axis is angled approximately 30 degrees from the horizontal plane, with the air then being drawn up through the coil and discharged at that angle from the horizontal plane. This does allow the outlet opening height to be somewhat reduced, but not to a significant degree.
With the draw-thru arrangement, it is also recognized by the Applicants that a nonuniform distribution of airflow at the inlet of the fan tends to reduce the performance level and create noise problems. That is, if the air is drawn up through the coil located in the lower portion of the casing and then turned 90 degrees to be discharged by the draw-thru fan, there will be significantly more air flowing through the lower portion of the fan than at the top portion, where the air has to travel further before it reaches the fan. Again, the tilted arrangement mentioned hereinabove will somewhat alleviate this problem, but it will still demonstrate reduced performance characteristics.
A scroll (i.e. squirrel cage) fan has been found to be practical for use in applications wherein it is desired to change the direction of airflow either before or after passing through the coil. This is true because of the inherent characteristics of such a fan. However, such a squirrel cage blower tends to use substantially more power than a propeller fan in moving the same amount of air. Accordingly, for such low static pressure conditions, a propeller fan is more economical and practical for use in outdoor fan applications.
It is therefore an object of the present invention to provide an improved fan arrangement for an outdoor coil of a thru-the-wall air conditioning unit.
Yet another object of the present invention is the provision in a thru-the-wall packaged air conditioning unit for improved airflow characteristics through the fan.
Still another object of the present invention is the provision for maximizing the height of an outdoor coil in a thru-the-wall air conditioning unit.
Still another object of the present invention is for a thru-the-wall air conditioning unit which is economical to manufacture and efficient in operation.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.